1. Field of the Invention
The present invention relates to a vehicular AC generator having a pair of Y-connection circuits.
2. Description of the Related Art
For a conventional vehicular three-phase generator as disclosed in, for example, Japanese Patent Application Laid-Open No. 58-218873 shown in FIG. 15, neutral-point diodes 23N and 25N configuring a neutral-point-current rectifying circuit are connected between a high-potential output side of a rectifier device 12 and a neutral point N of a stator coil 16 and between a low-potential output side of the rectifier device 12 and the neutral point N of the stator coil 16 and a three-phase voltage output of the stator coil 16 configured by a three-phase armature in which three windings Y are connected in a Y form is applied to rectifying diodes 23 and 25 of the rectifier device 12 for full-wave-rectifying the three phase voltage.
A vehicular three-phase generator has excellent characteristics in that output can be increased without increasing the size of the generator by providing the neutral-point-current rectifying circuit 12 having the neutral-point diodes 23N and 25N.
Specifically, the neutral-point diodes 23N and 25N are added to the rectifier device 12, so that an exciting current circulating through each winding Y and the rectifier device 12 is derived from the neutral point N of the stator coil 16 so as to be supplied to the stator coil 16 and the rectifier device 12, thereby improving the output of the generator. This type of vehicular three-phase generator is widely used at present.
The configuration of a conventional vehicular three-phase generator will be described below with reference to the accompanying drawings. FIG. 13 is a sectional side view of the conventional vehicular three-phase generator (hereafter referred to as an AC generator) and FIG. 14 is an internal view showing the interior of a rear bracket 2 shown in FIG. 13.
The AC generator includes a case 3 formed of an aluminum front bracket 1 and a rear bracket 2, a shaft 6 provided in the case 3 and having a pulley 4 fixed at one end thereof, a Landolt-type rotor 7 secured to the shaft 6, a fan 5 secured to the opposite side surfaces of the rotor 7, a stator 8 secured to an inner wall surface of the case 3, a slip ring 9 for supplying current to a rotor coil 13 fixed to the other end of the shaft 6, a pair of brushes 10 slidable on the slip ring 9, a brush holder 11 receiving therein the brushes 10, a rectifier device 12 electrically connected to a stator coil 16 for rectifying an AC voltage generated in the stator coil 16 into a DC voltage, a heat sink 19 fitted to the brush holder 11, and a regulator 20 connected to the heat sink 19 for adjusting the field current to be supplied to the stator coil 16 in accordance with the output of the generator.
The rotor 7 comprises the rotor coil 13 for generating a magnetic flux and a pole core 14 covering the rotor coil 13 and on which magnetic poles are formed by the magnetic flux. The pole core 14 is comprised of a pair of a first pole-core body 21 and a second pole-core body 22 engaged with each other. The first pole-core body 21 and the second pole-core body 22 are made of iron and are respectively provided with a plurality of pawl-shaped magnetic poles 21a and 22a. 
The stator 8 comprises a stator core 15 and a stator coil 16 in the form of a conductor made of copper and wound on the stator core 15. An AC voltage is generated due to the changing magnetic flux supplied from the rotor coil 13 in accordance with the rotation of the rotor 7. As shown in FIG. 14, a plurality of slots 17 are provided on the stator core 15 in the radial direction thereof with their open portions facing the axis of rotation, and the stator coil 16 is wound in each slot 17.
The rotor coil 13, stator coil 16, rectifier device 12 and regulator 20 normally generate heat while the generator generates power. A generator having a class 100A rated output current shows a calorific value of 60, 500, 120 or 6 W in the respective portions 13, 16, 12 and 20 at a relatively high-temperature rotation point.
To cool the heat produced by power generation, intake ports are provided in the front bracket 1 and the rear bracket 2, respectively, for taking in cooling air from the outside with the fan 5 set on the shaft 6. The cooling air taken in through the intake port of the rear bracket 2 passes through the rear-bracket-side heat sinks 24, 24 of the rectifier device 12 and a vent hole formed facing the regulator heat sink 19 to cool the rectifier device 12 and the regulator 20.
The cooling air cools the rectifier device 12 and the regulator 20 while passing through them, and is then directed in the centrifugal direction by the rear-bracket-side fan 5 to cool the rear-bracket-side stator coil end so as to be discharged to the outside through a bracket exhaust port.
Moreover, the cooling air drawn in the axial direction from the front-bracket-side intake port is directed in the centrifugal direction by the fan 5 to cool the front-bracket-side stator coil end and then discharged to the outside through a bracket exhaust port similar to the case of the rear bracket 2 side.
As shown in FIG. 14, the rectifier device 12 comprises the positive-pole-side heat sink 24 for supporting a plurality of positive-pole-side diodes 23 and a neutral-point diode 23N, a negative-pole-side heat sink 26 for supporting a plurality of negative-pole-side diodes 25 and a neutral-point diode 25N, and a circuit board 27 for electrically connecting anodes of the diodes 23 and 23N, cathodes of the diodes 25 and 25N, and the stator coil 16. A three-phase voltage generated in the stator coil 16 is full-wave-rectified by the rectifier device 12 having the diodes 23 and 25.
As shown in FIGS. 16 to 18, the rectifier device 12 including a heat sink and the like is configured so that the entirety thereof forms an approximate horseshoe shape. This configuration is used to store components by efficiently using the space in the generator because the shape of the generator is roughly cylindrical. As shown in FIGS. 16 and 17, the heat sinks 24 and 26 are made of aluminum or the like so as to radiate the heat produced by the diodes 23, 25, 23N, and 25N.
The heat sink 24 has a plurality of fins F protruding toward the rotor axis from the back of a joint surface between the positive-pole-side diodes 23 and 23N. Moreover, the heat sink 26 for joining the negative-pole-side diodes 25 and 25N is directly connected at its back side to the rear bracket 2 as a ground.
The diodes 23, 25, 23N, and 25N are molded, roughly rectangular and connected to the circuit board 27 by lead terminals protruding from one side of the diodes. The diodes 23, 25, 23N, and 25N are arranged on the heat sinks 24 and 26 in the radial direction so that they do not interfere with each other.
Among the diodes 23, 25, 23N, and 25N, the neutral-point diodes 23N and 25N are arranged so as to face a connector C for transferring a signal to and from the regulator 20 through the open portion of the slip ring.
Recently, in response to requests for increasing the output of AC generators due to the increased electric loads of vehicles, the output of generators has thus far been improved by adding a neutral-point diode to a full-wave rectifying circuit so as to derive an exciting current for circulating through windings and a full-wave rectifier device from the neutral point of a three-phase armature winding, and by using the exciting current with the three-phase armature winding and the full-wave rectifier device.
However, when a neutral-point diode is added to a full-wave rectifying circuit, a ripple current is output from the neutral-point diode and a ripple voltage is superimposed on a rectified output voltage and becomes power-supply noise, which affects other control components.
As for AC generators for improving output without using a neutral-point diode, it has been found that the pawl-like magnetic poles of the generator resonate at certain high-speed-rotational regions to cause undesirable electromagnetic noise. Therefore, the addition of a neutral-point diode, which is preferable for the above reason, is a technological contradiction.
Moreover, in vehicular AC generators, the rotor coil, stator coil, rectifier and regulator constantly produce heat under power generation. AC generators having a rated output current of class 100A shows a calorific value of 60, 500, 120 or 6 w in respective portions thereof at a relatively high-temperature rotation point, as referred to before, and hence electric circuitry is exposed to severe thermal conditions. Particularly, owing to the fact that the rectifier device is located at the cooling-air intake side of a rear-bracket-side cooling fan, and hence the cooling-air speed is low and the heat transfer characteristics are inferior, it is required that the rectifier device is equipped with a cooling heat sink.
However, the layout dimensions of the rectifier are limited by the arrangement of other components. Therefore, even if heat sinks at the positive-pole side and negative-pole side of diodes are enlarged in the range of the limited mounting space of the rectifier, the range of enlargement is limited.
Therefore, when adding not only diodes for full-wave rectification (hereafter referred to as full-wave rectifying diodes) but also a neutral-point diode to a heat sink having the limited enlargement range, the heat-sink area per full-wave rectifying diode is decreased and the cooling performance is deteriorated in order to ensure space for the neutral-point diode. When the cooling performance is deteriorated and the neutral-point diode is also used to improve the generated output, a problem occurs in that the amount of heat produced by the full-wave rectifying diodes are further increased.
Moreover, by adding the neutral-point diode, problems occur in that not only is the cooling performance deteriorated but also, other components cannot be arranged because of insufficient space or the cost increases due to the increased number of neutral-point diodes.
The present invention is intended to solve the above problems and has for its object to provide a vehicular AC generator capable of improving the generated output by preventing excessive heat generation while reducing ripples in the rectified output cased by the installation of neutral-point diodes.
Bearing the above object in mind, according to a first aspect of the present invention, there is provided a vehicular AC generator comprising: first and second Y-shaped three-phase connection stator windings having a Y-connection formed on a common stator core such that a pair of three windings have a phase difference of 30xc2x0 from each other; and a rectifier device comprising a first rectifier for rectifying and outputting a phase current derived from an end of each winding of the first Y-shaped three-phase connection stator winding and a neutral-point current derived from a neutral point of the first stator winding and a second rectifier for rectifying and outputting a phase current derived from an end of each winding of the second Y-shaped three-phase connection stator winding and a neutral-point current derived from a neutral point of the second stator winding, the first and second rectifiers each generating a synthesized output at an output terminal; wherein the first and second rectifiers each have phase-current rectifying diodes and neutral-point-current rectifying diodes disposed on a common heat sink.
In a preferred form of the first aspect of the invention, the neutral-point-current rectifying diodes of the first and second rectifiers are disposed on the heat sink at locations next to a phase-current rectifying diode which will reach the highest temperature among the phase-current rectifying diodes.
In another preferred form of the first aspect of the invention, the neutral-point-current rectifying diodes of the first and second rectifiers are disposed at opposite sides of the output terminal, and the phase-current rectifying diodes are disposed on the heat sink at locations next to each of the neutral-point-current rectifying diodes.
In a further preferred form of the first aspect of the invention, the neutral-point-current rectifying diodes of the first and second rectifiers are disposed at either a negative-pole side or a positive-pole side of the rectifiers.
According to a second aspect of the present invention, there is provided a vehicular AC generator comprising: first and second Y-shaped three-phase connection stator windings having a Y-connection formed on a common stator core so that a pair of three windings have a phase difference of 30xc2x0 from each other; and a rectifier device comprising a first rectifier for rectifying and outputting a phase current derived from an end of each winding of the first Y-shaped three-phase connection stator winding and a neutral-point current derived from a neutral point of the first stator winding, and a second rectifier for rectifying and outputting a phase current derived from an end of each winding of the second Y-shaped three-phase connection stator winding, the first and second rectifiers being each disposed to generate a synthesized output at an output terminal; wherein the first rectifier has phase-current rectifying diodes and the second rectifier has phase-current rectifying diodes and neutral-point-current rectifying diodes, the phase-current rectifying diodes of the first rectifier and the phase-current rectifying diodes and the neutral-point-current rectifying diodes of the second rectifier being disposed on a common heat sink.
In a preferred form of the second aspect of the invention, the neutral-point-current rectifying diodes of the second rectifier are disposed on a heat sink at locations next to a phase-current rectifying diode that will reach the highest temperature among the phase-current rectifying diodes.
In another form of the second aspect of the invention, the phase-current rectifying diodes of the first and second rectifiers are disposed at opposite sides of an output terminal on the heat sink, and the neutral-point-current rectifying diodes are disposed between the output terminal and the phase-current rectifying diodes.
In a further form of the second aspect of the invention, the neutral-point-current rectifying diodes of the second rectifier are disposed at either a negative-pole side or a positive-pole side of the second rectifier.
The above and other objects, features and advantages of the present invention will become more readily apparent from the following detailed description of a few preferred embodiment of the invention when taken in conjunction with the accompanying drawings.